1. Field of the Invention
The present invention relates to a local area network (LAN) system and a router unit used in a LAN system, and more particularly, to a LAN system interconnecting a central station and a plurality of subscriber terminals via a network, and also to a router unit used therein, to provide data communications services between the plurality of subscriber terminals via the central station by using logical and physical addresses assigned thereto, in addition to analog information delivery services from the central station to the plurality of subscriber terminals.
2. Description of the Related Art
In recent years, CATV-based local area network systems (CATV-LAN) are expected to be excellent infrastructures for data communications. To serve this expectation, however, it is necessary to solve some problems with the existing CATV-LAN systems as will be described below, and the present invention is intended to provide appropriate solutions for them.
Conventional CATV networks connect between a central station and a plurality of subscriber terminals to provide a unidirectional communications service for distributing analog information, such as voice and video programs, from the central station to the subscriber terminals. Today's CATV networks is added a backward communication function from the subscriber terminals to the central station, which enables subscriber's realtime participation in TV programs, pay-per-view accounting, and other new services. Most of such CATV networks use coaxial cables as broadband signal transmission media.
On the other hand, the increasing demands for data communications drive the CATV networks to expand their usage to digital data communications. This is an attempt to exploit the above-described excellent features of CATV networks--bidirectional communication capabilities between a central station and subscriber terminals and wide bandwidth provided by the coaxial cable media. More specifically, a CATV network can be used to interconnect many personal computers at the subscribers' sites via a central station, independently of the existing public telephone networks, allowing the subscribers to enjoy data communications services including high-speed access to the Internet.
Such bidirectional data communications services are usually provided in a LAN environment where the Internet Protocol (IP) is used for addressing the members in a network.
In such a LAN data communications environment, different IP addresses have to be properly set to subscriber terminals. However, since this address setting is left to individual subscribers, some subscriber may set up, by mistake, his/her own terminal with the same IP address as that of a terminal of someone else. This causes a collision of IP addresses in a network, which disrupts the operation of the network system.
There may also be a potential problem of illegal use of IP addresses, where some person may maliciously use another person's IP address to make access to the network resources by setting up his/her terminal as the other person's. This problem raises the demands for security systems to protect the network from such malicious person's intrusion into the network. Security issues are really inevitable in order to make the public use of a CATV-based network possible.
Some network protocols such as Dynamic Host Configuration Protocol (DHCP) are introduced recently, which provides automatic set up of IP addresses to prevent the system from address collision. This DHCP, however, does not serve as a protection device against deliberate change of IP addresses. Therefore, it is still impossible to prevent illegal use of other people's IP addresses from happening.